Moderate drinking has been associated with reduced cardiovascular morbidity, whereas heavy drinking has an opposite effect. We investigated the effect of ethanol (EtOH) on the cell survival promoting PI3 kinase/akt pathway in cultured human umbilical vein endothelial cells (HUVEC). Exposure of cells to low concentrations (2-20 mM) of EtOH resulted in rapid induction of Akt phosphorylation that could be prevented by pertussis toxin (PTX) or PI3 kinase inhibitors. Several downstream effectors of PI3 kinase/akt, including p70S6 kinase, glycogen synthase kinase 3 alpha/beta, and IkB-alpha, were also phosphorylated by EtOH, the latter resulting in a 3-fold activation of NFkappaB. EtOH also activated p42/44 MAP kinase in a PI3 kinase-dependent manner. EtOH (2-20 mM) increased endothelial NO synthase activity, which could be blocked by transfection of HUVEC with dominant negative Akt. The adenosine A1 receptor antagonist DPCX prevented Akt phosphorylation by 2-20 mM EtOH or adenosine. In contrast, incubation of HUVEC with high concentrations (50-100 mM) of EtOH resulted in mitochondrial permeability transition and caspase-3 activation, followed by apoptosis, as verified by DNA fragmentation and TUNEL assays. EtOH-induced apoptosis was unaffected by DCPX and was potentiated by PI3kinase inhibitors. Thus, low concentrations of EtOH activate the cell survival promoting PI3K/akt pathway in endothelial cells by an adenosine-dependent mechanism, and activation of the proapoptotic caspase pathway by high concentrations of EtOH via an adenosine-independent mechanism can mask or counteract such effects. These effects may be relevant to the bimodal effects of EtOH drinking on cardiovascular morbidity. Our previous study has indicated the existence of a novel cannabinoid (CB) receptor in vascular endothelium (Jarai et al., PNAS 96:14136, 1999). We recently found that the CB analog ?abnormal cannabidiol? (abn-cbd) does not bind to the two known CB receptors, CB1 and CB2, yet acts as a full agonist in relaxing rat isolated mesenteric artery segments. Vasodilation by abn-cbd is endothelium-dependent, PTX-sensitive, and is inhibited by the BKCa channel inhibitor charybdotoxin, but not by the NO synthase inhibitor L-NAME or the vanilloid VR1 antagonist capsazepine. The cannabidiol analog O-1918 does not bind to CB1 or CB2 receptors and does not cause vasorelaxation at concentrations up to 30 micromolar, but causes concentration-dependent (1-30 micromolar) inhibition of the vasorelaxant effects of abn-cbd and anandamide. In anesthetized mice, O-1918 dose-dependently inhibits the hypotensive effect of abn-cbd, but not of the CB1 agonist HU-210. In HUVEC, abn-cbd induces phosphorylation of protein kinase B/akt and p42/44 MAP kinase, which is inhibited by O-1918, by PTX and by PI3 kinase inhibitors. These findings indicate that abn-cbd is a selective agonist and O-1918 a novel, silent antagonist of an endothelial ?anandamide receptor? which is distinct from CB1 and CB2 receptors and is coupled thropugh Gi/Go to the PI3 kinase/akt signaling pathway.